1. Field of the Invention
The present invention relates to a structure and a manufacturing method of a rotary type motor in which coils are incorporated in the slots of a stator.
Further, the present invention relates to a motor which has coils of a plurality of phases for generating a rotating magnetic field at a stator and a manufacturing method for the stator and, more particularly, to a highly efficient compact lightweight motor ideally suited for an electric vehicle and a manufacturing method for a stator thereof.
2. Description of the Related Art
As shown in FIG. 2, a stator 2a of a rotary type motor such as a DC motor has a structure in which a plurality of coils 2c composed of wound copper wire or the like installed on a multilayer iron core 2b constructed by iron sheets. FIG. 3 shows the top view of a multilayer iron core 3a before the coils are installed. A typical multilayer iron core is made as follows: a silicon steel plate having a thickness of 0.3 mm to 0.5 mm is cut by electric discharge machining, pressing, etc., and shaped into an annular component provided with slots, namely, the grooves in which the coils are inserted, formed In the inner periphery thereof. Multiple of the annular components are stacked, and the inner diameters and slots thereof are aligned, then bonded by welding or caulking. Slots 3b through 3m are provided at equal intervals in the inner periphery of the multilayer iron core 3a; coils 4a as shown in FIG. 4 composed of wound and formed copper wires are installed in these slots. There is an alternative available method in which wire is directly wound in the slots to form the coils. The coil 4a shown in FIG. 4 has inserts 4b and 4c which are fitted in the slots of a stator, and coil ends 4d and 4e which are disposed at the top and bottom of the stator. Such a coil comes roughly in two types. In one type, a thick wire having a diameter of about 1.2 mm to about 3 mm is wound and the inserts are pressed to have rectangular shapes and aligned. In the other type, a thin wire having a diameter of 1.2 mm or less is wound, and the wires of the inserts are bundled and shaped. In either type, the coils are shaped before they are self-fused or the wires are bonded to each other with an adhesive agent. These coils are incorporated in the stator to make up a motor stator. Incidentally, the term "self-fusing" is a method in which a nylon or epoxy type resin is coated on the surfaces of wires in advance and it is melted by heating with current or hot air or by heating in a furnace so as to bond the wires to each other.
FIG. 5 shows how the coil 4a is inserted in the stator 5a. The two inserts 4b and 4c are fitted in two slots 5b and 5c in the inner periphery of the stator 5a. In the same manner, the coils are inserted in the other slots.
Lap winding is one of the structures for installation on the stator. FIG. 6 illustrates an example of a motor stator 6a which employs the lap winding structure for installing the coils. One coil is mounted on the stator in such a manner that it is spanned over two slots, and the two inserts of each coil are disposed on the inner side and outer side, respectively, in the slots in the radial direction of the stator. For instance, in the case of a coil 6b, inserts 6n and 6o are fitted in slots 6b' and 6e' over two slots 6c' and 6d'. One insert 6n is disposed on the inner side in the radial direction of the stator in the slot 6b' and the other insert 6o is disposed on the outer side in the radial direction of the stator in the slot 6e'. Next, inserts 6p and 6q of an adjoining coil 6c are fitted in slots 6c' and 6f' over two slots 6d' and 6e'. One insert 6p is disposed on the inner side in the radial direction of the stator in the slot 6c' and the other insert 6q is disposed on the outer side in the radial direction of the stator in the slot 6f'. In the same manner, the adjoining coils 6d through 6m are installed in slots 6d' through 6m' by lapping them clockwise to complete the winding structure which is evenly shaped in the circumferential direction of the stator 6a. This lap winding structure, however, has a major disadvantage: since the inserts of the individual coils 6b through 6m are disposed on the inner and outer sides of the slots, it is necessary to pull out the inserts of the three coils 6b through 6d which have been disposed on the inner sides of the slots and to install the inserts of the other three coils 6k through 6m on the outer sides of the slots. This process for uninstalling the coils requires much time and involves high possibility of damaging the coating of wires, thus posing a big bottleneck in manufacturing motors.
To solve the problem with the coil uninstalling process, a stator 7a having a modified lap winding structure shown in FIG. 7 has been devised. This structure employs three types of coils having different shapes, namely, coils 7b through 7d, coils 7k through 7m, and coils 7e through 7j. First, both inserts of the coils 7b through 7d are installed so that they are positioned on the outer sides of slots 7b' through 7g', then the coils 7e through 7j are inserted in slots 7e' through 7m' in order clockwise. Thus, one insert of each of the coils 7e through 7j is disposed on the inner side in the radial direction of the stator, while the other insert thereof is disposed on the outer side in the radial direction of the stator. The coils 7b through 7d will have been installed on the outer sides of slots 7k' through 7d' before inserting last three coils 7k through 7m; hence, both inserts of each of the coils 7k through 7m are respectively installed on the inner sides of the slots 7k' through 7d'. As described above, this structure allows the coils to be inserted in the stator in succession without the need for the coil uninstalling process. The structure requires, however, that the three different types of coils, namely, 7b through 7d, 7e through 7j, and 7k through 7m having different shapes, are manufactured separately, and the inserting sequence based on the type of coils is observed. Further, the stator 7a develops uneveness in the circumferential direction thereof, leading to uneven revolution of the motor incorporating the stator due to uneven magnetic field.
The foregoing lap winding and modified lap winding use the structure wherein two coil inserts 8a and 8b are installed in one slot 8c and the coils are arranged in the radial direction of the stator as shown in FIG. 8. In either winding structure, an open-slot stator, which permits easier installation of coils, is normally used. Immediately after a coil has been inserted in a slot or after the coils have been inserted in all slots, paper or a magnetized wedge or wedges 8d are placed in an inlet or inlets 8e of a slot or slots to secure the coil or coils.
(1) FIG. 9 illustrates a stator 9a having a structure wherein coils 9b through 9j are inserted clockwise in slots 9b' through 9m' and the last three coils are left uninserted. In the case of the lap winding, the two inserts of each coil are disposed side by side in a slot in the radial direction of the stator as illustrated by 8a and 8b of FIG. 8. For this reason, by the time the last three coils, not shown, are inserted in slots 9k', 9l', 9m', 9b', 9c', and 9d', the inserts 9n, 9o, and 9p on one side of the three coils 9b, 9c and 9d which have been installed first will have already been disposed on the inner sides of the slots 9b', 9c', and 9d', thus preventing the insertion of the coils on the outer sides of the slots. Hence, it is necessary to conduct the so-called coil uninstalling work for temporarily removing the coil inserts 9n, 9o, and 9p disposed on the inner sides of the slots 9b', 9c', and 9d' from the slots. After uninstalling the coil inserts, the inserts of the coils to be installed last (not shown) are installed on the outer sides of the slots 9b', 9c', and 9d', the other inserts being disposed on the inner sides of the slots 9k', 9l', and 9m'. Then, the inserts 9n, 9o, and 9p which have been uninstalled are reinstalled on the inner sides of the slots 9b', 9c', and 9d'. The coil inserts are about 97 to about 99% as wide as the slots, so that uninstalling the coils which have been inserted are very likely to cause the side surfaces or edges of the slots to scratch the coils. In addition, since the inserts 9n, 9o, and 9p are positioned in an interior 9q of the stator after uninstalling them from the slots, they take up the working space for inserting the last three coils. This makes it difficult and time-consuming to insert the last three coils. There are cases where the inserts 9n, 9o, and 9p of the coils 9b, 9c, and 9d are temporarily left in the interior 9q of the stator without inserting them in the slots 9b', 9c', and 9d' in order to prevent damage to the coating caused by installing and uninstalling the coils; however, the coils temporarily left uninserted hinder the insertion of all other coils, thus requiring a lot of time for completing the installation of the coils. In FIG. 9, the lap winding structure wherein a coil is inserted over two slots has been employed to explain the problem involved in the structure. The same applies to a lap structure wherein one coil is spanned over a different number of slots. As the number of slots over which a coil is spanned, increases the area of the inner periphery required for uninstalling coils increases, resulting in more difficult insertion or even making insertion impossible in some cases.
(2) As means for solving the problem of uninstalling the coils described above, the modified lap winding shown in FIG. 7 has been devised. In this structure, both inserts 7b" and 7b'", 7c'" and 7c'", and 7d" and 7d'" of three coils 7b, 7c, and 7d to be installed first are disposed on the outer sides of slots 7b' through 7g' , while both inserts 7k'" and 7k'", 7l" and 7l'", and 7m" and 7m'" of three coils 7k, 7l, and 7m to be installed last are disposed on the inner sides of slots 7k' through 7d'. As previously mentioned, both inserts of each of the coils 7b, 7c, and 7d are inserted in order at the outer sides of slots 7b' through 7g', then coils 7e through 7j are inserted clockwise in the slots 7g' through 7m' in the lap winding fashion, beginning with a slot 7e'. Lastly, both inserts of each of the coils 7k, 7l, and 7m are inserted at the inner sides of the slots 7k' through 7d', thus allowing all coils to be inserted without the need for uninstalling coils. In this structure, however, the way the coils are inserted differs depending on the slots, and it is therefore required to make three different types of coils, namely, the coils 7b through 7d to be inserted first, the coils 7k through 7m to be installed last, and the coils 7e through 7j to be installed between the former two groups of coils. This also involves a disadvantage in that the coils must be installed while checking the shapes of each coil and the inserting sequence. The structure, therefore, is advantageous in that it reduces the chance of damage to the coils caused by installing and uninstalling the coils to and from the slots, but it is not necessarily superior to the standard lap winding from the standpoint of the total time and cost for manufacturing a stator. In addition, since the shapes of the coils and the way they are inserted are different, the finished stator is uneven in the circumferential direction. The result is an uneven magnetic field with uneven revolution of the motor incorporating the stator.
(3) In both the lap winding structure and modified lap winding structure, the coils are usually installed on an open-slot stator. In the case of an open-slot, there is less magnetic flux at the inlet of the slot and the efficiency of the motor is lower accordingly. Further, during the installation, the coils which have already been inserted often come out of the slots, adding to the difficulty in the installation work.
In a conventional manufacturing method for a motor of a few tens of watts or less, enameled wire is directly wound on a stator, then a coil end is shaped for finish to make the coil end compact. A motor having a larger output is usually manufactured as follows: former winding is finished in advance and both sides of an insert are forcibly fitted by an inserter at the same time in a slot radially toward the outside diameter thereof. In this case, semi-closed slots are normally used. The former-wound wires are disturbed in alignment at the time of insertion and they are inserted with the wires crossing. Even for coils of two phases or more, formers designed with no difference for different coil shapes are used to perform winding. When all coils of one phase have been inserted in a core, the coils are set down about the portions near the edge surface of the core toward the outside diameter of the core to shape the coil ends for each phase so as to allow the coils of the next phase to be inserted. Then, after all coils have been inserted, the coil ends of the coils inserted first, which coil ends have been pushed toward the outside diameter of the stator core, and the coil ends of the coils inserted last, which coil ends have remained at the inside diameter side, are compressed and shaped in the radial and axial directions, thereby making the coil ends compact.
The conventional inserting method and coil end finishing method, however, inevitably place restrictions in achieving further compactness of coil ends. This is because the insertion based on direct winding or the use of an inserter has a restricted occupancy. According to the inserting method, occupancy of 70% is usually the limit because of the disturbance attributable to the crossing of wires that occurs at the time of insertion. Moreover, in the coil end shaping process, the extra length of the coil ends required for inserting a coil or for allowing the next coil to be inserted is compressed to a certain extent, and the length of the coil ends contributing greatly to loss remains unchanged.